linux-kernel - Re: [malware-list] TALPA - a threat model? well sorta.

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Date:	Fri, 15 Aug 2008 07:12:56 +0200
From:	Johannes Weiner <hannes@...urebad.de>
To:	david@...g.hm
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Theodore Tso <tytso@....edu>,
	Christoph Hellwig <hch@...radead.org>,
	Eric Paris <eparis@...hat.com>, tvrtko.ursulin@...hos.com,
	alan@...rguk.ukuu.org.uk, andi@...stfloor.org,
	linux-kernel@...r.kernel.org, malware-list@...ts.printk.net,
	malware-list-bounces@...sg.printk.net, peterz@...radead.org,
	viro@...IV.linux.org.uk
Subject: Re: [malware-list] TALPA - a threat model?  well sorta.

Hi,

david@...g.hm writes:

> On Thu, 14 Aug 2008, Arjan van de Ven wrote:
>
>> On Thu, 14 Aug 2008 22:04:00 -0400
>> Theodore Tso <tytso@....edu> wrote:
>>
>>> On Thu, Aug 14, 2008 at 06:44:33PM -0700, david@...g.hm wrote:
>>>> could you do something like defining a namespace inside posix
>>>> attributes and then setting up a mechanism in the kernel to alert
>>>> if the attributes change (with the entire namespace getting cleared
>>>> if the file gets dirtied)?
>>>
>>> According to Eric Paris the clean/dirty state is only stored in
>>> memory.  We could use the extended attribute interface as a way of not
>>> defining a new system call, or some other interface, but I'm not sure
>>> it's such a great match given that the extended attributes interface
>>> are designed for persistent data.
>>>
>>> I agree that doesn't actually work very well for the tracker use case,
>>> where you the clean/dirty bit to be persistent (in case the tracker is
>>> disabled due to the fact you are running on battery, for example, and
>>> then you reboot).
>>>
>>
>> but we need a "give me all dirty files" solution, not a "is this file
>> dirty" solution.
>>
>> I do not want a virus scanner to constantly have to poll the whole fs
>> for dirty files ;-)
>
> I'm not sure.
>
> there are two situations (with the transition between them)
>
> 1. unscanned system, we want to do everything. (this happens
> immediatly after a new signature file is deployed)
>
> here you do just want to filter out the files that have been scanned
> from the list of everything, and you probably want to check at the
> time of scanning the file in case it was opened (and scanned) in the
> meantime.
>
> 2. mostly scanned system, we only want to scan files that have been
> dirtied.
>
> here you don't need to scan everything, you only need to scan in two cases
>
> 2a. the file was dirtied (you learn about it and add it to the queue
> of files to scan when you get around to it)
>
> 2b. an unscanned file is opened (the library detects that the file was
> not marked approved by all the current scanners, so it invokes the
> scanners on this file before completing the open, or copy for mmap, or
> whatever)

2b could also be used as a general lazy scanning mechanism, no?  If
there is a new signature or the file is dirty or unknown, scan it.
Always.

So this should all just be one case, no?

	Hannes
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